This invention relates generally to field emission displays, and, more specifically, to a method and apparatus for controlling the brightness of a pixel by controlling the temperature of a temperature sensor in the pixel.
In field emission displays, fast response time and high contrast are best achieved by active matrix designsxe2x80x94i.e., designs that employ a current switching device, conventionally one or more transistors, at each pixel of the display.
Conventional active matrix displays are fabricated on either a silicon substrate or a dielectric (typically glass) substrate.
An active matrix flat panel display having transistors fabricated from single-crystal silicon on a silicon substrate currently is feasible only for small displays. For a display area larger than several square centimeters, it is impractical to produce such a large transistor array without excessive defects, and such a large silicon substrate is undesirably fragile.
An active matrix flat panel display having thin film transistors (TFT""s) fabricated on a glass substrate is much more suitable for a large area display. Such TFT designs are conventionally used for liquid crystal displays because they overcome the stated shortcomings of displays fabricated on silicon substrates. However, TFT designs are much less suitable for field emission displays, because thin film transistors typically have much higher leakage current than single-crystal silicon transistors. This leakage current is acceptable for liquid crystal displays, but not for field emission displays, because the latter are current-controlled rather than voltage-controlled and typically have time-averaged pixel currents on the order of only 10xe2x88x928 ampere or less.
Accordingly, there is a need for a field emission display that overcomes the shortcomings of single-crystal transistor arrays on silicon substrates and TFT arrays on dielectric substrates.
The invention is an active matrix display that does not require a transistor or similar current switching device at each pixel. Instead, the display employs in each pixel a temperature-controlled current source which provides to the field emitters of the pixel an amount of electrical current that varies in response to the temperature of a temperature sensor. Each pixel further includes a thermoelectric heat transfer circuit which transfers heat to or from the sensor in an amount that varies in response to the video signal. Consequently, the video signal controls the temperature of the sensor within a pixel""s temperature-controlled current source, which controls the current flow through the pixel""s field emitters.